Chain length of cationic alpha-helical peptide sufficient for gene delivery into cells

Coordinating antigen cytosolic delivery and danger signaling to program potent cross-priming by micelle-based nanovaccine

Although re-activating cytotoxic T-cell (CTLs) response inside tumor tissues by checkpoint blockade has demonstrated great success in tumor immunotherapy, active induction of efficient endogenous CTL response by therapeutic vaccines has been largely hampered by inefficient cytosolic delivery of antigens and coordinated activation of dendritic cells (DCs) in lymph nodes. Here we show that polyethylene glycol-phosphatidylethanolamine (PEG-PE) micelles transform soluble peptides into α-helix to enable their efficient cytosolic delivery. The same PEG-PE micelles also serve as chaperon of TLR4 signaling to coordinate its adjuvant effect on the same DCs. Furthermore, these nanovaccines effectively target lymph node DCs. Thus, PEG-PE micelle vaccines program at multiple key aspects for inducing strong CTL responses and build up a foundation for combinational tumor therapy.

Effect of monomer sequence of poly(histidine/lysine) catiomers on gene packing capacity and delivery efficiency

This work presents a novel method to synthesize reducible polycations with specific monomer sequence, and provides new insight on how a monomer sequence of the polymeric catiomer will affect its gene packing capacity and delivery efficiency.

Immunogenicity of a bovine herpesvirus 1 glycoprotein D DNA vaccine complexed with bovine neutrophil beta-defensin 3

Protective efficacy against bovine herpesvirus 1 (BoHV-1) has been demonstrated to be induced by a plasmid encoding bovine neutrophil beta-defensin 3 (BNBD3) as a fusion construct with truncated glycoprotein D (tgD). However, in spite of the increased cell-mediated immune responses induced by this DNA vaccine, the clinical responses of BoHV-1-challenged cattle were not reduced over those observed in animals vaccinated with the plasmid encoding tgD alone; this might have been because the vaccine failed to improve humoral responses. We hypothesized that an alternative vaccine design strategy that utilized the DNA vaccine pMASIA-tgD as a complex with BNBD3 might improve humoral responses while maintaining robust Th1-type cell-mediated responses. C57BL/6 mice were vaccinated with pMASIA-tgD complexed with 0, 0.01875, 0.1875, or 1.875 nmol of a stable synthesized analog of BNBD3 (aBNBD3). The best results were seen in mice immunized with the vaccine composed of pMASIA-tgD complexed to 0.1875 nmol aBNBD3. In this group, humoral responses were improved, as evidenced by increased virus neutralization, tgD-specific early IgG1, and later IgG2a titers, while the strong cell-mediated immune responses, measured based on specific gamma interferon (IFN-γ)-secreting cells, were maintained relative to pMASIA-tgD. Modulation of the immune response might have been due in part to the effect of BNBD3 on dendritic cells (DCs). In vitro studies showed that murine bone marrow-derived DCs (BMDCs) pretreated with aBNBD3 were activated, as evidenced by CD11c downregulation, and were functionally mature, as shown by increased allostimulatory ability. Native, synthetic, and analog forms of BNBD3 were equally capable of inducing functional maturation of BMDCs.

Human-protein-derived peptides for intracellular delivery of biomolecules

Access of therapeutic biomolecules to cytoplasmic and nuclear targets is hampered by the inability of these molecules to cross biological membranes. Approaches to overcome this hurdle involve CPPs (cell-penetrating peptides) or protein transduction domains. Most of these require rather high concentrations to elicit cell-penetrating functionality, are non-human, pathogen-derived or synthetic entities, and may therefore not be tolerated or even immunogenic. We identified novel human-protein-derived CPPs by a combination of in silico and experimental analyses: polycationic CPP candidates were identified in an in silico library of all 30-mer peptides of the human proteome. Of these peptides, 60 derived from extracellular proteins were evaluated experimentally. Cell viability and siRNA (small interfering RNA) transfection assays revealed that 20 out of the 60 peptides were functional. Three of these showed CPP functionality without interfering with cell viability. A peptide derived from human NRTN (neurturin), which contains an α-helix, performed the best in our screen and was uniformly taken up by cultured cells. Examples for payloads that can be delivered to the cytosol by the NRTN peptide include complexed siRNAs and both N- and C-terminally fused pro-apoptotic peptides.

Structural rearrangements and chemical modifications in known cell penetrating peptide strongly enhance DNA delivery efficiency

Amphipathic peptides with unusual cellular translocation properties have been used as carriers of different biomolecules. However, the parameters which control the delivery efficiency of a particular cargo by a peptide and the selectivity of cargo delivery are not very well understood. In this work, we have used the known cell penetrating peptide pVEC (derived from VE-cadherin) and systematically changed its amphipathicity (from primary to secondary) as well as the total charge and studied whether these changes influence the plasmid DNA condensation ability, cellular uptake of the peptide-DNA complexes and in turn the efficiency of DNA delivery of the peptide. Our results show that although the efficiency of DNA delivery of pVEC is poor, modification of the same peptide to create a combination of nine arginines along with secondary amphipathicity improves its plasmid DNA delivery efficiency, particularly in presence of an endosomotropic agent like chloroquine. In addition, presence of histidines along with 9 arginines and secondary amphipathicity shows efficient DNA delivery with low toxicity even in absence of chloroquine in multiple cell lines. We attribute these enhancements in transfection efficiency to the differences in the mechanism of complex formation by the different variants of the parent peptide which in turn are related to the chemical nature of the peptide itself. These results exhibit the importance of understanding the physicochemical parameters of the carrier and complex in modulating gene delivery efficiency. Such studies can be helpful in improving peptide design for delivery of different cargo molecules.

Delivery of intracellular-acting biologics in pro-apoptotic therapies

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide "stapling", cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.

High-content screening of peptide-based non-viral gene delivery systems

High-content screening (HCS) uses high-capacity automated fluorescence imaging for the quantitative analysis of single cells and cell populations. Here, we developed an HCS assay for rapid screening of non-viral gene delivery systems as exemplified by the screening of a small library of peptide-based transfectants. These peptides were simultaneously screened for transfection efficiency, cytotoxicity, induction of cell permeability and the capacity to transfect non-dividing cells. We demonstrated that HCS is a valuable extension to the already existing screening methods for the in vitro evaluation of non-viral gene delivery systems with the added value that multiple parameters can be screened in parallel thereby obtaining more information from a single screening event, which will accelerate the development of novel gene delivery systems.

A new family of peptide-nucleic acid nanostructures with potent transfection activities

A family of His-rich peptides has been shown to complex DNA and efficiently deliver these nucleic acids into eukaryotic cells. Therefore, these nanoscale complexes have potential applications in gene therapy. Here, we review a number of spectroscopic and biophysical investigations aimed at characterizing the supramolecular interactions of the peptides with the nucleic acids and when overcoming the membrane barriers of the cell. Furthermore, solid-state NMR distance measurements for the first time reveal close interatomic distances between the amino acid side chains and the DNA phosphates within the transfection complex. A recent study indicates that the peptides are also potent transfectants of siRNAs and they could thereby be of potential interest for gene silencing therapies using these compounds. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.

Development of a slow non-viral DNA release system from PDLLA scaffolds fabricated using a supercritical CO2 technique

Polyamidoamine polymers (PAA) comprising methylene-bisacrylamide/dimethylethylene-diamine monomers were synthesized, complexed with DNA and incorporated into porous P(DL)LA scaffolds by using a supercritical CO(2) (scCO(2)) technique. Scaffolds were made in a dry state consequently there was a need to lyophilize the complexes. A statistically significant reduction of the transfection efficiency was observed in the absence of trehalose when compared to the original complex after freeze-drying. Increasing concentrations (0-10% w/v) of trehalose were added to the complex prior to freeze-drying. Structure dependent differences in DNA binding were evaluated by gel electrophoresis and thermal transition analysis. TEM and PCS showed aggregate formation after freeze-drying without trehalose. Scaffolds were characterized by pore sizes of 173 +/- 73 microm and a porosity of 71%. The transfection potential of the released DNA was investigated by seeding scaffolds with A549 cells and following firefly luciferase as a marker gene after 48 h exposure. Low but continuous levels of transfection were observed for PAA complexes during a 60-day study. Complexes made with Lipofectaminetrade mark gave initially higher levels of DNA release but no further expression was seen after 40 days. Uncomplexed DNA showed background levels of transfection. Culturing cells on 3D scaffolds showed a benefit in retention of transfection activity with time compared to 2D controls. Transfection levels could be increased when cells were grown in OptiMEM. This study demonstrated that PAA/DNA complexes incorporated into a P(DL)LA scaffold made by using scCO(2) processing exhibited a slow release and extended gene expression profile.

Synthetic PEGylated glycoproteins and their utility in gene delivery

PEGylated glycoproteins (PGPs) were synthesized by copolymerizing a Cys-terminated PEG-peptide, glycopeptide, and melittin peptide. Compositionally unique PGPs were prepared by varying the ratio of PEG-peptide (20-90%) and melittin (0-70%) with a constant amount of glycopeptide (10%). The PGPs were purified by RP-HPLC, and characterized for molecular weight and polydispersity by GPC-HPLC and SDS-PAGE and for composition by RP-HPLC following reduction to form monomeric peptides. PGPs formed DNA condensates of 200-300 nm in diameter that were administered to mice via the tail vein. Biodistribution studies confirmed their primary targeting to liver hepatocytes with a DNA metabolic half-life of 1 h. Upon stimulation by hydrodynamic dosing with saline, PGP DNA (5 microg) mediated luciferase expression in the liver detected by bioluminescence imaging (BLI) after 24 h. The level of gene expression mediated by PGP DNA was 5000-fold less than direct hydrodynamic dosing of an equivalent amount of DNA and was independent of the mol percent of melittin incorporated into the polymer, but dependent on the presence of galactose on PGP. The results establish the ability to prepare three-component gene delivery polymers that function in vivo. Further design improvements in fusogenic peptides for gene delivery and for the simultaneous use of a nuclear targeting strategy will be necessary to approach levels of expression mediated by the direct hydrodynamic dosing of DNA.

Cationic amphipathic histidine-rich peptides for gene delivery

Besides being a useful tool in research, gene transfer has a high potential as treatment for a variety of genetic and acquired diseases. However, in order to enable a gene to become a pharmaceutical, efficient and safe methods of delivery have to be developed. We recently found that cationic amphipathic histidine-rich peptide antibiotics can efficiently deliver DNA into mammalian cells. Our lead compound, LAH4 (KKALLALALHHLAHLALHLALALKKA), demonstrated in vitro transfection efficiencies comparable to those of commercially available reagents. Synthesis and evaluation of LAH mutants provided evidence that the transfection efficiency depends on the number and positioning of histidine residues in the peptide as well as on the pH at which the in-plane to transmembrane transition takes place. Moreover, recent results suggest that binding of the DNA complexes to the plasma membrane is mediated by heparan sulfate proteoglycans and that anionic phospholipids may be involved in the endosomal destabilization process. Finally, we also describe in this review the rationale that led to the development of LAH4 as a DNA carrier as well as the biophysical methods that have allowed us to propose a model which could explain the way this peptide destabilizes the endosomal bilayer.

Mechanistic aspects of CPP-mediated intracellular drug delivery: relevance of CPP self-assembly

In recent years, cell-penetrating peptides have proven to be an efficient intracellular delivery system. The mechanism for CPP internalisation, which first involves interaction with the extracellular matrix, is followed in most cases by endocytosis and finally, depending on the type of endocytosis, an intracellular fate is reached. Delivery of cargo attached to a CPP requires endosomal release, for which different methods have recently been proposed. Positively charged amino acids, hydrophobicity and/or amphipathicity are common to CPPs. Moreover, some CPPs can self-assemble. Herein is discussed the role of self assembly in the cellular uptake of CPPs. Sweet Arrow Peptide (SAP) CPP has been shown to aggregate by CD and TEM (freeze-fixation/freeze-drying), although the internalised species have yet to be identified as either the monomer or an aggregate.

Secondary conformation of short lysine- and leucine-rich peptides assessed by optical spectroscopies: effect of chain length, concentration, solvent, and time

Solution secondary structures of three synthetic cationic peptides, currently used in antisense oligonucleotide delivery into living cells, have been analyzed by means of circular dichroism (CD) and Raman scattering in different buffers as a function of concentration and time. All three peptides are of minimalist conception, i.e., formed by only two types of amino acids (leucine: L and lysine: K). Two of these peptides contain 15 aminoacids: N(ter)- KLLKLLLKLLLKLLK (L(10)K(5)), N(ter)-KLKLKLKLKLKLKLK (L(7)K(8)), and the third one has only 9 residues: N(ter)-KLKLKLKLK (L(4)K(5)). The conformational behavior of the 15-mers in pure water differs considerably one from another. Although both of them are initially disordered in the 50-350 microM range, L(10)K(5) gradually undergoes a disordered to alpha-helix transition for molecular concentrations above 100 microM. In all other solvents used, L(10)K(5) adopts a stable alpha-helical conformation. In methanol and methanol/Tris mixture, nonnative alpha-helices can be induced in both KL-alternating peptides, i.e., L(7)K(8) and L(4)K(5). However, in major cases and with a time delay depending on peptide concentration, beta-like structures can be gradually formed in both solutions. In PBS and methanol/PBS mixture, the tendency for L(7)K(8) and L(4)K(5) is to form structures belonging to beta-family. A discussion has been undertaken on the effect of counterions as well as their nature in the stabilization of ordered structures in both KL-alternating peptides.

Cationic compounds used in lipoplexes and polyplexes for gene delivery

Gene transfer represents an important advance in the treatment of both genetic and acquired diseases. Many cationic lipids and cationic polymers naturally occurred or synthesized have been used for gene transfer. They have the advantages over viral gene transfer as non-immunogenic, easy to produce and not oncogenic. These cationic compounds, however, have the major limitations of inefficient transfection and toxicity to cells. For overcoming these problems, many new cationic compounds were developed since the first cationic lipid, DOTMA, was found usage in gene therapy. This article reviews cationic lipids for gene therapy from chemistry viewpoint and we classify these compounds as monovalent cationic lipids, polyvalent cationic lipids, cationic polymers, guanidine containing compounds, cationic peptides and cholesterol containing compounds, and hope to provide suggestions on the development of this variety of cationic compounds through the discussion.

An overview of current delivery systems in cancer gene therapy

The main objective in gene therapy is the development of efficient, non-toxic gene carriers that can encapsulate and deliver foreign genetic materials into specific cell types such as cancerous cells. During the past two decades, enormous research in the area of gene delivery has been conducted worldwide, in particular for cancer gene therapy application. Viral vectors are biological systems derived from naturally evolved viruses capable of transferring their genetic materials into the host cells. Many viruses including retrovirus, adenovirus, herpes simplex virus (HSV), adeno-associated virus (AAV) and pox virus have been modified to eliminate their toxicity and maintain their high gene transfer capability. The limitations associated with viral vectors, however, in terms of their safety, particularly immunogenicity, and in terms of their limited capacity of transgenic materials, have encouraged researchers to increasingly focus on non-viral vectors as an alternative to viral vectors. Non-viral vectors are generally cationic in nature. They include cationic polymers such as poly(ethylenimine) (PEI) and poly(L-lysine) (PLL), cationic peptides and cationic liposomes. The newly described liposomal preparation LPD (liposomes/protamine/DNA), for example, has shown superiority over conventional liposomes/DNA complexes (lipoplexes). Although non-viral vectors are less efficient than viral ones, they have the advantages of safety, simplicity of preparation and high gene encapsulation capability. This article reviews the most recent studies highlighting the advantages and the limitations of various types of gene delivery systems used in cancer gene therapy.

Long circulation of intravenously administered plasmid DNA delivered with dendritic poly(l-lysine) in the blood flow

We previously showed that dendritic poly(L-lysine) of the 6th generation (KG6) had high transfection ability without significant cytotoxicity in vitro. Here, to evaluate the potential of KG6 as a nonviral gene carrier that works in vivo, we investigated the biodistribution of plasmid DNA delivered with KG6 in mice after intravenous administration, in comparison with DOTAP/Chol liposomes and PEI. Southern blotting analysis revealed that plasmid DNA complexes with KG6 at a C/A ratio of 8.0 circulated in the blood for 3 h after intravenous injection. The amounts of plasmid DNA in the liver gradually decreased. In tumor-bearing mice, plasmid DNA injected with KG6 was observed in the tumor at 60 min after the intravenous injection, while no DNA was present in the tumor using DOTAP/Chol liposomes. The stealth character of DNA complexes with KG6 in the blood would cause an enhanced permeability and retention (EPR) effect in the tumor. KG6 is expected to be a promising candidate that enables functional gene delivery in vivo.

Amphipathic peptides and drug delivery

The discovery of cell-penetrating peptides as gene delivery systems and the interest in the mechanism by which these vectors cross the cell membrane have generated a large number of studies. Among the parameters involved in the translocation process, controversy has arisen about the role of the amphipathicity of the carriers in the interaction and reorganization of the cell membrane. In this review we have summarized the vectors with primary or secondary amphipathicity related to secondary structure. Some of the insights into the relationship between the aggregation state of the peptide at the concentrations used for internalization studies and its interaction with the cell membrane result from our contribution to the field with a new family of amphipathic proline-rich peptides.

Novel poly(ethylene glycol) derivatives with carboxylic acid pendant groups: synthesis and their protection and enhancing effect on non-viral gene transfection systems

Novel carboxylic acid pendant-containing poly(ethylene glycol) (PEG) derivatives (PEG-Cs) were synthesized by the chemical modification of the carbon-carbon double-bond side chain of copoly(allyl glycidyl ether/ethylene oxide) (copoly(AGE/EO)). PEG-C showed a protecting ability for the DNA/polycation complex from the albumin-induced aggregation. It also expressed the enhanced efficiency on the polycation-mediated gene transfection on the cultured cells (up to 3-4-times higher), probably due to its disperse-stabilizing property and also the proton-sponge effect.

Complexes of plasmid DNA with basic domain 47-57 of the HIV-1 Tat protein are transferred to mammalian cells by endocytosis-mediated pathways

Arginine-rich peptides, penetratins, as part of a number of cellular and viral proteins, can penetrate across plasma membrane directly, without participation of endocytosis. We show that one of penetratins, the basic domain 47-57 of human immunodeficiency virus, type 1, transcription factor Tat (Tat peptide), is able to interact with plasmid DNA electrostatically. These interactions result in formation of polyelectrolytic complexes at various negative/positive charge ratios of plasmid DNA and Tat peptide. Plasmid DNA is capable of binding to Tat peptide up to 1.7-fold excess of the complex positive charge. The DNA-Tat complexes can be used for delivery of plasmid DNA into mammalian cells. Transfection efficacy of cultured cells by DNA-Tat complexes is stimulated by free Tat peptide, most likely because it protects DNA-Tat complexes from disruption by anionic proteoglycans of cellular surface. Our data strongly argue in favor of the endocytosis-dependent mechanism of DNA-Tat complex uptake by mammalian cells similarly to internalization of complexes of plasmid DNA with other polycationic carriers. Moreover, different cell lines use different endocytosis-mediated pathways for DNA-Tat complex internalization. Intravenous injections to mice of DNA-Tat complexes in comparison with injections of naked DNA showed an inhibitory effect of DNA-Tat complex positive charge on expression of transferred gene. A low level of foreign gene expression in the liver of mice injected intravenously with positively charged DNA-Tat complexes is accounted for by inactivation of DNA-Tat complexes in the bloodstream due to their interactions with serum albumin. These data should be taken into account in an attempt to develop versatile gene delivery systems based on penetratin application for human disease therapy.

Mimovirus: a novel form of vaccine that induces hepatitis B virus-specific cytotoxic T-lymphocyte responses in vivo

CD8(+) cytotoxic T lymphocytes (CTLs) are now recognized as important mediators of immunity against intracellular pathogens, including human immunodeficiency virus and tumors. How to efficiently evoke antigen-specific CTL responses in vivo has become a crucial problem in the development of modern vaccines. Here, we developed a completely novel CTL vaccine-mimovirus, which is a kind of virus-size particulate antigen delivery system. It was formed by the self-assembly of a cationic peptide containing 18 lysines and a CTL-epitope peptide of HBsAg(28-39), with a plasmid encoding mouse interleukin-12 (IL-12) through electrostatic interactions. We examined the formation of mimovirus by DNA retardation assay, DNase I protection assay, and transmission electron microscopy and demonstrated that mimovirus could efficiently transfer the plasmid encoding IL-12 into mammalian cells such as P815 cells in vitro. Furthermore, it was proved that mimovirus could induce an HBsAg(28-39)-specific CTL response in vivo. Considering its effectiveness, flexibility, and defined composition, mimovirus is potentially a novel system for vaccination against intracellular pathogens and tumors.

Vectorial delivery of macromolecules into cells using peptide-based vehicles

The ability to direct the import of therapeutic agents into cells and target them to specific organelles would greatly enhance their functional efficacy. The available spectrum of peptide-based import signals and intracellular routing signals might provide practical solutions towards achieving a guided or vectorial delivery of molecules. Multiple cell-targeting signals and routing domains can be efficiently displayed on branched peptides. These constructs are typically nonimmunogenic in the absence of adjuvant and can be easily assembled using solid phase synthesis. The vectorial delivery of larger complexes, however, will necessitate the development of alternate templates that favor the optimal presentation of all functional signals.

Translocating peptides and proteins and their use for gene delivery

A dramatic surge in the development of peptides for gene delivery in vitro and in vivo has been witnessed in the past decade. A better understanding of the structural and mechanistic properties of peptides has been an important step for the rational design of optimal peptide-based gene delivery systems. Research has focused on the design of short synthetic peptides that overcome both extracellular and intracellular limitations of other gene delivery systems by binding reversibly and condensing DNA, specifically targeting cells and/or tissues, rapidly releasing plasmids into the cytoplasm and mediating efficient nuclear translocation.